Just to recap: you moved home. Different room, nearly twice the size and with, as you describe them, cardboard walls instead of brick.
Those are very fundamental differences, and yet although some responders have suggested the room, it seems all the focus has been on the power supply, and questioning whether the amp is OK. Whilst I understand that the comparison with the Cyrus is part of what makes you suspect the amp, and there is certainly no harm at all in trying to borrow another amp to verify, it seems to me that the elephant in the room is still the room itself.
In my original response I suggested if possible trying in another room in the flat as similar as possible in dimensions to your old listening room, which would give you an idea of the effect purely of room size, though not construction. (That could still be something worth doing, despite the hassle.) And the construction of the walls may be very significant, as they could be far more absorbing at the bass end than your old walls. Quite what the solution is if it is indeed the room is harder to fathom. I find descriptions of Naim amps at the bass end odd, as their specs don’t indicate any difference, but people seem to experience greater bass extension (as opposed to just better bass control) as you go up the range, but whatever the reason, if that is the case the greater bass drive needed in the bigger room with absorbent walls might need an amp with greater bass ability than the 250.
However you have now changed speakers, though with no information as to how you chose the Dynaudios and how you know they suit your taste and room. (if you had talked about changing speakers people likely would have suggested trying at home, when you could be sure that whatever you bought would work.) The new speakers presumably have better bass capability than your old ‘bookshelf’ speakers (I don’t recall what they were), which might be expected to give you a better chance in the bigger room.
That brings me to the crux: re-reading the thread, you haven’t talked at all about experimenting with room layout, notably speaker and listening positions, yet they can make a huge difference. If I were you I would get a copy of REW (“Room Equalisation Wizard”) software, which is available free of charge, and a measuring microphone (the one REW recommend is good and relatively inexpensive), and do some room measurements to start to find out what is going on in the room, and play with positioning. There is another current thread with someone exploring speaker positioning, which may give some food for thought. (What do you think? Speaker placement advice)